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3 years ago

How many protons and electrons are in an atom of sodium whose atomic number is 11?

1 answer:

6 0

Atomic number is also known as proton number, so it would have 11 protons. Assuming you mean a neutral atom, it will have to have an equal number of electrons to protons, so it has 11 electrons too

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How long will it take for a 750 mg sample of radium with a half life of 15 days to decay to exactly 68mg?

weqwewe [10]

Answer:

52 da

Step-by-step explanation:

Whenever a question asks you, "How long to reach a certain concentration?" or something similar, you must use the appropriate integrated rate law expression.

The integrated rate law for a first-order reaction is

ln([A₀]/[A] ) = kt

Data:

[A]₀ = 750 mg

[A] = 68 mg

t_ ½ = 15 da

Step 1. Calculate the value of the rate constant.

t_½ = ln2/k Multiply each side by k

kt_½ = ln2 Divide each side by t_½

k = ln2/t_½

= ln2/15

= 0.0462 da⁻¹

Step 2. Calculate the time

ln(750/68) = 0.0462t

ln11.0 = 0.0462t

2.40 = 0.0462t Divide each side by 0.0462

t = 52 da

8 0

3 years ago

Fun, Easy Question! 15 points! Is salt less dense or more dense than water?

jasenka [17]

A salt is more dense than water if it is insoluble in water

7 0

2 years ago

Read 2 more answers

Thallium has two stable isotopes, 203tl and 205tl. knowing that the atomic weight of thallium is 204.4, which isotope is the mor

Elza [17]

You have to figure out a way to write the two unknown abundances in terms of one variable.

The total abundance is 1 (or 100%). So if you say the abundance for the first one is X then the abundance for the second one has to be 1-X (where X is the decimal of the percentage so say 0.8 for 80%).

203(X) + 205(1-X) = 204.4

Then you just solve for X to get the percentage for TI-203.
And then solve for 1-X to get the percentage for TI-205.

After that the higher percentage would be the most abundant.

203x + 205 - 205x = 204.4
-2x + 205 = 204.4
-2x = -0.6

x = 0.3
1-x = 0.7

Then the TI-205 would have the highest percentage and would be the most abundant.

7 0

2 years ago

Barium sulfate is made by the following reaction.

ipn [44]

Answer:

%age Yield = 96 %

Explanation:

The balance chemical equation for given double replacement reaction is,

Ba(NO₃)₂ + Na₂SO₄ → BaSO₄ + 2 NaNO₃

Step 1: Calculate moles of Ba(NO₃)₂:

Moles = Mass / M.Mass

Moles = 75.1 g / 261.33 g/mol

Moles = 0.2873 moles of Ba(NO₃)₂

Step 2: Find out moles of BaSO₄ formed:

According to balance chemical equation,

1 mole of Ba(NO₃)₂ produced = 1 mole of BaSO₄

So,

0.2873 moles of Ba(NO₃)₂ will produce = X moles of BaSO₄

Solving for X,

X = 0.2873 mol × 1 mol / 1 mol

X = 0.2873 moles of BaSO₄

Step 3: Calculate Theoretical Mass of BaSO₄:

Mass = Moles × M.Mass

Mass = 0.2873 mol × 233.38 g/mol

Mass = 67.07 g of BaSO₄

Step 4: Calculate %age Yield as:

Theoretical Yield = 67.07 g

Actual Yield = 64.4 g

%age Yield = ???

Formula Used:

%age Yield = (Actual Yield ÷ Theoretical Yield) × 100

Putting Values,

%age Yield = (64.4 g ÷ 67.07 g) × 100

%age Yield = 96.01 % ≈ 96 %

6 0

2 years ago

When do you have to wear safety glasses while in lab?

never [62]

At all times when a lab is being operated no matter what the circumstances

6 0

2 years ago